Layered structure, sensor and method of producing and use of the same

ABSTRACT

The invention concerns a layered structure comprising at least two material layers. The layered structure is formed of a conductive polymer on a substrate material layer to allow a reaction in the conductive polymer material when the layered structure is exposed to the surrounding conditions. The invention also concerns a method for producing layered structure. In the method the conductive polymer material is applied on the substrate material by printing or spraying or stamping or casting or spin coating or by using photolithographic or laser ablation method or a combination of these. The invention further concerns a sensor comprising an electric device short circuited by the conductive polymer of the layered structure. In the sensor a change in the conductive polymer initiates a change in the function of the electric device.

BACKGROUND

The present invention relates to a layered structure comprising at leasttwo material layers, a sensor, a method for producing layered structureand its use.

Conductive polymers are materials which have been made conductive bydoping with suitable substance. In the doping process both electronacceptors and donors react with polymer structure resulting in highlyconducting derivatives. These reactions are called ‘doping’ in analogyto semiconductors, though they are closer to solid-state chemicalreactions. Another method for generating electrical conductivity inpolymers is blending in which conductive polymer and insulating materialare mixed. Electrical properties of conductive polymers can be changedover the fall range of conductivity from insulators to metallicconductors. An example of a conductive polymer is polyaniline which is asynthetic organic polymer obtained by the chemical or electrochemicaloxidative polymerization of aniline. Emeraldine base, which is the moststable insulating form of polyaniline, can be made conducting either byoxidation or by expose of functional protonic acids e.g. HCl or H₂SO₄.Correspondingly, the conducting emeraldine can be made less conductingor even insulating by a dedoping reaction caused by a reduction processor by exposure to alkaline materials. There are wide prospects of usingconductive polymers in variety of consumer products. Examples of knownuse of conductive polymers are batteries, electrical circuits,capacitors, EMI shields, organic LEDs, corrosion prevention products andantistatic products for use in e.g. package industry, construction,clothes, automotive industry, mining.

Conductive polymers, materials and products are known in the art frommany patent publications of which some of them are disclosed in thefollowing.

U.S. Pat. No. 5,783,111 discloses compositions comprising electricallyconducting polyaniline and particular substituted aromatic compoundsthat simultaneously form hydrogen bonds and ring-ring interactions with,respectively, the NH-groups and the six-membered rings of the conductingpolyanilines. The conducting polyaniline compositions show drasticallyenhanced processibility and their blends with insulating orsemiconducting materials exhibit significantly improved electricalproperties.

U.S. Pat. No. 5,656,081 discloses a press for printing an electricalcircuit component directly on a substrate with an electricallyconductive liquid. A method of making such a press includes the steps ofproviding a press surface and engraving the press surface with theplurality of liquid carrying cells which are in liquid communicationwith each other in both the printing direction and in the transversedirection.

U.S. Pat. No. 5,622,652 discloses electrically conductive liquid fordirectly printing an electrical circuit component onto a substrate and amethod for making such a liquid. The invention relates to anelectrically conductive liquid which, when printed onto a substrate iscapable of carrying out an electrical circuit function. Using the methodthere is no need for post-printing steps such as metal etching,catalytic ink activation or electroless deposition.

SUMMARY

The object of the present invention is to provide a novel layeredstructure comprising active substrate and conductive polymer material.

Another object of the present invention is to provide a method forproducing the layered structure comprising active substrate andconductive polymer material.

A further object of the present invention is to provide a sensorcomprising layered structure according to the invention.

In view of achieving of the objectives stated above the layeredstructure according to the invention is mainly characterized in that thelayered structure is formed of a conductive polymer on a substratematerial layer to allow a reaction in the conductive polymer materialwhen the layered structure is exposed to the surrounding conditions.

The method for producing layered structure is characterized by applyingthe conductive polymer material on the substrate material by printing orspraying or stamping or casting or spin coating or by usingphotolithographic or laser ablation method or a combination of these.

The sensor according to the invention comprising an electric deviceshort circuited by the conductive polymer of the layered structure ischaracterized in that a change in the conductive polymer initiates achange in the function of the electric device.

The layered structure according to the invention, comprising at leasttwo material layers, is formed of a conducting polymer on a substratematerial layer and said substrate material has the property ofcatalysing changes in the conductive polymer when the layered structureexperiences a change in its surrounding environment. Further, saidsubstrate material causes a dedoping reaction in the conductive polymer.

In the layered structure according to the invention the substratematerial allows a reaction in a conductive polymer, such as polyaniline,and the conductivity and/or optical property and/or color of theconductive polymer changes when the layered structure becomes exposed tothe surrounding conditions, e.g. to open air or humidity. The parametersaffecting the reaction are e.g. substrate material properties, such asacidity, porosity and thickness, as well as surrounding conditions, suchas humidity, UV radiation and temperature, and also properties of thelayered structure such as coating. By adjusting the surface or contactbetween the substrate material and conductive polymer it is possible toaffect the rate of the reaction. Coating and coating methods also affectthe reaction. This phenomenon found in the layered structure accordingto the invention can be utilized in various ways. In the layeredstructure the substrate material is paper or material with at least onecomponent of paper or other substrate material with suitable properties.

Geometrical properties of the polymer layer in the layered structurealso affect the rate of the reaction and thus the time dependentbehaviour of the conductivity of the conductive polymer. The thinner theconductive polymer layer the faster the conductivity decreases whenexposed to the surrounding conditions. By adjusting the horizontal andvertical dimensions of the conductive polymer layer it is possible tochoose the time scale during which the desired reaction occurs. Thisphenomenon has been demonstrated in FIG. 5.

Manufacturing methods for the layered structure in which conductivepolymer material is added on substrate surface according to theinvention are e.g. the conventional methods for manufacturing ofelectrical circuits, such as photolithography, spin coating, spraying,laser ablation, and casting as well as printing methods such as gravure,flexographic, offset, digital, or silk screen printing method or acombination of these. Layered structure according to the invention canalso be made using lamination, stamping, coating and vacuum coatingtechniques.

Utilizing the present invention makes it possible to produce inexpensiveindicator components printed on substrate material. These components canbe widely used for example in consumer products. The elasticity of thelayered structure gives it flexural strength which allows its use inapplications in which the layered structure may be bent. One of the mainadvantages of the present invention is that the phenomenon occurring inthe layered structure is detectable visually as well as instrumentally.

Examples of the use of the components according to the invention are thefollowing:

-   -   sensor material which indicates a charge in a state of a package    -   sensor material which indicates a change in a content of a        package    -   a sensor indicating conductivity change for example when a        package has been broken    -   entertaining applications in which a figure appears or        disappears when a package has been opened

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in detail withreference of the figures in the accompanying drawing:

FIG. 1A shows an example of a layered structure according to theinvention.

FIG. 1B shows a layered structure with a coating layer.

FIG. 2 shows a printing system for producing the layered structures.

FIG. 3A shows an application of the layered structure according to theinvention.

FIG. 3B shows another application of the layered structure according tothe invention.

FIG. 3C shows a cross-cutting of the layered structure application.

FIG. 4A shows an example of a sensor according to the invention.

FIG. 4B shows a cross cutting of the sensor according to the invention.

FIG. 5 shows an example of measured values of the change in resistancein the patterns formed of the layered structure according to theinvention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1A shows an example of a layered structure according to theinvention. The layered structure L comprises a substrate layer S and aconductive polymer layer P. The substrate layer S is paper or otherfiber based material or a substrate material with suitable propertiesaccording to the invention.

Optionally, an intermediate layer is generated between the substratelayer S and conductive polymer layer P. This intermediate layer adjuststhe reaction rate in the conductive polymer layer P by enabling ordisabling the passage of the environment factors to the layeredstructure L. The intermediate layer may also be an integral part of thesubstrate layer S.

FIG. 1B shows a layered structure with a coating layer T. In the coatinglayer T there is shown a breakage B through which the layered structureis exposed to the surrounding conditions. In the area of the breakage Bthe resistance of the conductive polymer layer P starts increasing. Thischange in resistance can be measured using conventional measurementdevices and also the change in colour of the conductive polymer can bedetected visually. Even through the example of FIG. 1B shows the coatinglayer T on top of the conductive polymer layer P, it is to be understoodthat the coating layer T can alternatively be on top of the substratelayer S or on both sides of the layered structure L.

FIG. 2 shows an example of a printing system in which the layeredstructure according to the invention is produced. The web W of substratematerial enters the printing unit 100 which comprises an impressioncylinder 10, a printing cylinder 20 and a container 40. The surface ofthe printing cylinder 20 is provided with printing elements 50. The inkcontainer 40 contains conductive polymer material liquid which is passedvia the printing elements 50 on the web W to form layered structures 30according to the invention. The printing system comprising a printingcylinder may be a gravure printing system, flexographic printing system,an offset printing system, or an electrographic printing system. Alsoother printing methods can be applied according to the invention, e.g.digital or silk screen printing method or stamping as well as sprayingand casting methods.

By using printing systems for manufacturing layered structures accordingto the invention it is possible to create structures comprisingconductive polymers of any desired dimensions and variable thickness.

The printing system 100 may also contain a curing unit 60 which curesthe web W by e.g. thermal curing or UV curing or other known curingmethod. The curing unit 60 may be placed on either side of the web or onboth sides.

FIG. 3A shows another application of the layered structure according tothe invention. In this layered structure application A1 wire w forms acontinuous pattern packed in small area. The change in resistance of thewire w catalysed by the substrate S is measured using the measuringequipment M and information of the change of resistance is achieved.

FIG. 3B shows an application of the layered structure according to theinvention. In this application A2 wires w₁, . . . , w_(n) composed ofthe conductive polymer are printed on the substrate layer S and they areelectrically connected in parallel. The total resistance of the parallelconnection of the wires w₁, . . . , w_(n) is measured using themeasuring equipment M which is e.g. a typical resistance meter. When thelayered structure L is exposed to the surrounding conditions theresistance of the wires w₁, . . . , w_(n) changes and this change givesinformation of how long the exposure has taken place.

FIG. 3C shows a magnified cross-cutting of the layered structureapplication A2. FIG. 3C shows the vertical variance in thickness ofwires w₁, . . . , w_(n). The first wire w₁ possesses the greatestvertical thickness and therefore the reaction causing the change ofconductivity in the layered structure according to the invention occursslowest. In the less thick wires w₂, . . . , w_(n) the reaction isfaster and depends in each wire on the vertical amount of the conductivepolymer in the wires. Therefore the total resistance increases graduallyin a non-linear or step-wise manner and the total time elapsed from theexposure of the layered structure application to the surroundingconditions can be estimated in fairly good accuracy. The change inresistance of the wires w₁, . . . , w_(n) is also detectable visually bythe change of the colour of the wires.

By varying the thickness and/or width of the wires w₁, . . . , w_(n) thereaction rate can be adjusted in a desired way. This way the time scalein which the reaction occurs can be chosen depending the purpose or useof the layered structure application A2.

FIG. 4A shows an example of a sensor according to the invention and FIG.4B shows a cross cutting of the sensor. The sensor 70 comprises anelectric device which in this example is a conventional RF tag C_(A)printed or manufactured on the substrate material S using any knownmethod. This type of an RF tag may act as an alarm means in a package.The RF tag C_(A) comprises a conductive polymer layer P which, with thesubstrate layer S, forms a layered structure according to the invention.The conductive polymer layer P is covered with the coating layer T. Aslong as the conductive polymer layer P is intact, it is in conductivestate and the RF tag C_(A) is short circuited. Once the layeredstructure becomes exposed to the surrounding conditions through abreakage conductive polymer P loses its conductivity due to the reactioncharacteristic for the layered structure according to the invention.This causes the RF tag C_(A) turning into an RF circuit which isreadable with any known RF tag indicating method. The signal given bythe RF circuit indicates the breakage of the package.

When the RF tag C_(A) is attached on a package the condition of thepackage can be monitored in any state of e.g. the transport chain orstorage. The monitoring gives information of the breakage of the packageor unauthorised opening of the package depending the positioning of thesensor on the package surface.

Other applications of the invention are e.g. use as sensor materialwhich indicates a change in a content of a package, such ascontamination. Also entertaining applications in which a figure appearsor disappears when a package has been opened can be accomplished usingthe invention.

Trial runs have been made in a pilot printing machine with the methodaccording to the invention and promising results have been achieved. Agravure cylinder was manufactured for the trial runs. The gravurecylinder contained line and pattern structures of various dimensions.The cell depths of the gravure cylinder were 22 μm, 33 μm, 45 μm, 80/85μm and 140/160 μm. The achieved line widths of the conductive polymervaried from 60 μm to 1 mm and the thickness of the conductive polymervaried from 0.1 to 10 μm. The machine speed of the pilot printingmachine in the trial runs was up to 100 m/min.

The gravure cylinder was used in the printing machine and threedifferent conductive polymer materials were used in printing onpolyester film with external chemical treatment and on a paper. The inkmaterials were polytiophene in a form of PEDT/PSS dispersion, SOL-GELPEDOT liquid and polyaniline based PANI/DBSA toluene. In the trial runspaper and polyester film proved to be a suitable substrate material forconductive polymer components. All tested conductive polymer materialswere found to be suitable for printing in the test printing machine.

The behaviour of the printed structures was followed for some time inthe printed material. It was found out that the conductivity of theprinted polyaniline patterns was changed in time and at the same timethe colour of the printed patterns was changing. When the substratematerial was paper the color and the conductivity were changing. Whenthe substrate material was a polyester film only a minor change wasdetected during the followed period.

FIG. 5 shows the measured change in resistance in the layered structureaccording to the invention. Four samples of polyaniline printed on paperwere followed for 250 hours. The thickness of the samples varied so thatthe sample 1 in FIG. 5 was thinnest and the sample 4 was thickest. Thesamples were kept in the plastic bag for the first 139 hours and thenthey were left in open air. In the sample 4 with the thickest layer ofpolyaniline the reaction occurred slowest and no big change is seen. Inthe samples 1, 2, 3 with thinner layer of polyaniline the reaction wasfaster depending on the layer thickness. Curves in FIG. 5 show clearlythe change in resistance when the samples are moved to open air.

In the following the patent claims will be given and various details ofthe invention may show variation within the scope of the invented ideadefined in the patent claims and differ from the details disclosed abovefor the sake of example only.

1. A layered structure, comprising: at least two material layersdefining the layered structure, said layered structure being formed of aconductive polymer material layer on a substrate material layer,wherein: the substrate material layer is paper, the conductive polymermaterial layer has been printed or coated on the substrate materiallayer, said substrate material layer has a property of catalyzing adedoping reaction in the conductive polymer material layer when thelayered structure experiences at least one of open air, a change inhumidity, and UV radiation, and horizontal and vertical dimensions ofthe conductive polymer material layer varies in different parts of theconductive polymer material layer.
 2. The layered structure according toclaim 1, wherein the conductive polymer material layer is polyaniline.3. The layered structure according to claim 1, wherein the layeredstructure comprises an intermediate layer between the substrate materiallayer and the conductive polymer material layer.
 4. The layeredstructure according to claim 1, wherein a reaction causing a change inthe layered structure is detectable in a change of a conductivity of theconductive polymer material layer.
 5. The layered structure according toclaim 1, wherein a reaction causing a change in the layered structure isdetectable visually in a change of the conductive polymer materiallayer.
 6. The layered structure according to claim 1, wherein a reactioncausing a change in the layered structure is detectable optically. 7.The layered structure according to claim 1, wherein the conductivepolymer material layer forms an electric circuit on the substratematerial layer.
 8. A method of producing the layered structure accordingto claim 1, comprising: applying the conductive polymer material layeron the substrate material layer by one of printing, spraying, stamping,casting, spin coating, by using photolithographic method and a laserablation method.
 9. The method according to claim 8, further comprising:printing the conductive polymer material layer on the substrate materiallayer by a printing system including a method of at least one ofgravure, flexographic, offset, digital, and silk screen printing. 10.Electric circuits manufactured according to the method of claim 8,wherein the electric circuits act as indicators.
 11. Sensorsmanufactured according to the method of claim
 8. 12. Entertainingproducts manufactured according to the method of claim
 8. 13. A sensor,comprising: an electric device short circuited by the conductive polymermaterial layer of the layered structure according to claim 1, wherein achange in the conductivity of the conductive polymer material layerinitiates a change in a function of the electric device.
 14. The sensoraccording to claim 13, wherein the conductive polymer material layer ofthe layered structure loses a conductivity when exposed to surroundingconditions, and activates the electric device.
 15. The sensor accordingto claim 13, wherein the electric device is an RF tag.
 16. The sensoraccording to claim 13, wherein the RF tag is wirelessly readable.